1. Field of the Invention
The present invention relates to a sheet discharge apparatus which sequentially discharges and stacks a sheet onto a stack tray, and a sheet processing apparatus and an image forming apparatus which have the sheet discharge apparatus.
2. Description of Related Art
A sheet processing apparatus in a related art which handles a sheet, such as a stapling device which staples a sheet bundle and a punching device which punches the sheet bundle, has a stack tray which sequentially stacks the sheet thereonto, and a discharge roller which discharges the sheet onto the stack tray (see Patent Documents 1 and 2 (Japanese Patent Application Laid-Open Nos. 10-181988 and 10-194569)).
FIG. 24 is a block diagram of a discharge portion of the sheet processing apparatus in Patent Documents 1 and 2. As illustrated in FIG. 24, the sheet processing apparatus in the related art has a pair of conveying rollers 1007 (a conveying roller 1007a and a conveying roller 1007b), a processing tray 1130, and a stack tray 1200. The sheet processing apparatus has a pair of left and right aligning members 1140 in the sheet width direction, a pair of discharge rollers 1180, a swinging guide 1150, and a drawing-in paddle 1160.
The pair of conveying rollers 1007 convey a sheet S from an upstream conveying path. The processing tray 1130 receives the conveyed sheet S. The stack tray 1200 stacks the processed and discharged sheet bundle thereonto.
Roulette belts are wound around the lower conveying roller 1007a of the pair of conveying rollers 1007 in several positions in the axial direction between the lower conveying roller 1007a and the conveying roller 1007b. A sheet guide is arranged in an appropriate position between the roulette belts.
The downstream side (or the upper left side in the drawing) in the discharge direction of the sheet S of the processing tray 1130 is inclined upward, and the upstream side (or the lower right side in the drawing) thereof is inclined downward. A trailing end stopper 1131 is provided at an upstream end of the processing tray 1130. The pair of discharge rollers 1180 (bundle discharge rollers 1180a and 1180b) are arranged on the downstream side of the processing tray 1130. The swinging guide 1150 has the upper bundle discharge roller 1180b on the lower surface at its end, and supports the upper bundle discharge roller 1180b so as to bring it into contact with or bring it out of contact with the lower bundle discharge roller 1180a. The drawing-in paddle 1160 is disposed above an intermediate portion.
The discharged sheet S is started to move to the trailing end stopper 1131 by its own weight. The paddle 1160 which has stopped in the home position is rotated counterclockwise to promote movement of the sheet. The trailing end of the sheet S is reliably abutted on the stopper 1131 and is then stopped. Rotation of the paddle 1160 is also stopped. The sheet is aligned by the aligning member 1140.
All the sheets of a first bundle are discharged onto the processing tray 1130 and are then aligned. The swinging guide 1150 is lowered so that the roller 1180b rides on the sheet bundle. The sheet bundle is stapled by a stapler which is on standby on the trailing end stopper 1131 and is then discharged onto the stack tray 1200.
During that time, a sheet S1 discharged from an image forming apparatus body is wound around a large conveying roller provided in the upstream portion of the processing tray 1130. Up to three sheets are reserved so as not to convey other sheets to the processing tray 1130.
Three sheets S2 in the large conveying roller portion directly pass through the upstream conveying path and are then conveyed to the processing tray 1130. The lowered swinging guide 1150 receives the three sheets S2 by the rollers 1180a and 1180b. After the trailing ends of the sheets S2 have passed through the pair of conveying rollers 1007, the rollers 1180a and 1180b are reversely rotated. Before the trailing end of the sheet S2 is abutted on the stopper 1131, the swinging guide 1150 is raised so that the roller 1180b is brought out of contact with the surface of the sheet. Like the operation of the first bundle, the fourth sheet or later passes though the upstream conveying path and is then discharged onto the processing tray in the state that the swinging guide 1150 is opened. The third bundle or later is aligned by the same operation as that of the second bundle. A set number of bundles are stacked onto the stack tray 1200 for end.
The bundle return angle of the pair of discharge rollers 1180 is slightly larger than the angle of the processing tray 1130 relative to the horizontal plane. The three overlapped sheets are abutted on the lower portion of the stopper 1131 to prevent sheet buckling. Any curled sheets can be easily aligned.
In Patent Document 2, in a sort process in a non-stapling mode, a small number of sheets (or two to five sheets) for one bundle are stacked and aligned on the processing tray 1130 to discharge the bundle onto the stack tray 1200. The stacking properties on the stack tray 1200 can be improved.
In Patent Documents 1 and 2, when the sheets stacked on the inclined processing tray are discharged by the bundle discharge rollers, the angle of the conveying direction (or the nip angle) of the bundle discharge rollers is typically slightly larger (1 to 2°) than the angle of the processing tray. The angle of the processing tray typically has an inclination of approximately 35° relative to the horizontal plane in consideration of the sheet aligning properties and shortening of time required for alignment. The sheet is reversely conveyed from the bundle discharge rollers in the direction of the trailing end stopper so as to follow the surface of the processing tray. In consideration of the aligning properties, the discharge and stacking time, and the stacking shape, the stack tray is set to an angle slightly closer to the horizontal plane than the processing tray (or approximately 30° relative to the horizontal plane in the related art).
The sheet discharge direction is larger than 25° relative to the horizontal plane in consideration of the basis weight (ream weight) of the sheet, the use environment, and the curled state.
When the angle of the discharge direction is larger than the angle of the stack tray, there has been known that the discharge properties are deteriorated due to floating of the leading end of the sheet by air resistance and unstability of the posture at discharge and falling. To perform stable discharge, the discharge portion typically sets the angle of the discharge direction to 20 to 22° relative to the horizontal plane, and brings the leading end of the sheet into contact with the surface of the stack tray before the trailing end of the sheet passes through the discharge nip portion to perform stable discharge control. The stability when each sheet is discharged can be maintained. When the sheet bundle is discharged, the weight applied to the leading ends of the sheets is increased to push out the stacked sheet. The discharge of the sheet bundle of a large number of sheets can block the discharge port.
In Patent Document 2, the sheet is discharged at an angle larger than the inclination angle of the stack tray (35°). After the trailing end of the sheet has passed through the nip between the bundle discharge rollers, the posture at discharge and falling onto the stack tray can be unstable. In consideration of this, the bundle of a small number of overlapped sheets is always discharged to increase the weight of the discharged sheet bundle, thereby improving the discharge stability.
The angle of the discharge direction is large (approximately 35 to 36°). A small number of light and thin sheets or a small number of sheets with the leading end curled upward are overlapped, resulting in stacking failure. In consideration of the floating of the leading end of the sheet at discharge and the unstability of discharge and falling properties, increase of the discharge speed is limited. A bundle of a plurality of sheets which have been always stacked once on the processing tray 1130 is discharged. The stacking and aligning processes on the processing tray during the interval of sheet conveying need to be completed. Faster discharge is thus difficult.
The present invention provides a sheet discharge apparatus, a sheet processing apparatus, and an image forming apparatus, which can improve the aligning and stacking properties and cope with a wide range of types and sizes of sheets and higher speed.